To the Editor: In the absence of either effective treatment or effective vaccines, reducing transmission-related behavior is the most practical means of trying to control the acquired immunodeficiency syndrome (AIDS) epidemic. Intravenous drug users constitute the second largest group of persons with AIDS in the United States; 2249 of the 13,216 U.S. cases have intravenous drug use as their primary risk factor, and an additional 1144 have both intravenous drug use and male homosexuality as risk factors. Furthermore, in the United States, intravenous drug users are the primary source of transmission to heterosexuals and to children (AIDS Activity, Centers for . . .